Lepton mass effects and angular observables in $\Lambda_b \to \Lambda (\to p \pi) \ell^+\ell^-$

TL;DR

This paper investigates the decay $ ext{Lambda}_b o ext{Lambda} ( o p ext{pi}) ext{l}^+ ext{l}^-$, including lepton mass effects, to explore angular observables and potential signs of lepton flavor universality violation in baryonic decays.

Contribution

It provides a complete set of ten angular observables for the baryonic decay mode, incorporating finite lepton mass effects and highlighting unique asymmetries sensitive to new physics.

Findings

At least one angular asymmetry remains non-zero in the large recoil limit.

The decay mode offers a new avenue to test lepton flavor universality.

Finite lepton mass effects are significant in analyzing angular observables.

Abstract

The flavor changing rare decay $B\to K^{*}(\to K\pi)\ell^+\ell^-$ is one of the most studied modes due to its sensitivity to physics beyond the standard model and several discrepancies have come to light among the plethora of observables that are measured. In this paper we revisit the analogous baryonic decay mode $\Lambda_{b}\rightarrow \Lambda (\to p\pi) \ell^{+}\ell^{-}$ and we present a complete set of ten angular observables that can be measured using this decay mode. Our calculations are done retaining the finite lepton mass so that the signal of lepton non-universality observed in $B\to K^{*} \ell^+\ell^-$ can be corroborated by the corresponding baryonic decay mode. We show that due to the parity violating nature of the subsequent $\Lambda\to p\pi$ decay there exist at least one angular asymmetry that is non-vanishing in the large recoil limit unlike the case in $B\to K^{*}\ell^+\ell^-$ decay mode, making it particularly sensitive to new physics that violates lepton flavor universality.